Recent Death:
* Shell: The shell will still be intact, but may have a slightly duller appearance.
* Body: The soft body will be visible inside the shell, but may appear pale or discolored.
* Smell: There may be a slight fishy smell, but it won't be strong.
Longer Time Since Death:
* Shell: The shell may become brittle and crack easily.
* Body: The body will start to decompose and may be obscured by algae or other debris.
* Smell: There will be a strong, foul odor.
Other Clues:
* No movement: Obviously, a dead snail will not be moving.
* Lack of response: If you gently tap the shell, a live snail will usually retract into its shell. A dead snail will not respond.
Important Note: It's important to remove dead snails from your tank as soon as possible. They can release harmful bacteria that can harm other fish and invertebrates.